The invention relates to a valve for controlling liquids. One such valve is known from European Patent Disclosure EP 0 477 400 A1. There, the actuating piston of the valve member is disposed, tightly displaceably, in a smaller-diameter portion of a stepped bore, while a larger-diameter piston, which is moved with the piezoelectric actuator, is disposed in a larger-diameter portion of the stepped bore. Fastened between the two pistons is a hydraulic chamber, in such a way that when the larger piston is moved a certain distance by the actuator, the actuating piston of the valve member executes a stroke that is lengthened by the step-up ratio of the stepped bore diameter.
In such valves, the problem arises of compensating for changes in length of the piezoelectric actuator, the valve, or the valve housing through the hydraulic coupling chamber, hereinafter called the pressure chamber for short. Since to open the valve the piezoelectric actuator generates a pressure in the pressure chamber, this pressure also causes a loss of liquid in the pressure chamber. To prevent the pressure chamber from being pumped dry, refilling is necessary. Devices that solve this problem are indeed already known, but no valve is provided in them to monitor the refilling, or is it stated whether the supply medium can be resupplied.